Electric fuse



June 10, 19 F. s. KLEIN ELECTRIC FUSE Filed May 6, 1958 INV EN TOR.

'ing the end part of an arranged to form a substan-' Patented June 10, 1941 UNITED STATES PATENT OFFICE 2,245,345 ELECTRIC FUSE Franklin S. Klein, Malverne, N. Y. Application May 6, 1938, Serial No. 206,473 (Cl. 200-121) 9 Claims.

This invention relates to electric fuses which form a fusible link in an electric circuit.

The object of the invention is to provide an improvement in enclosed fuses whereby the fusible link cannot be tampered with or renewed, or reinforced, or any form of metal used to rees tablish the circuit through the fuse case; and because these fuses are useless after one rupture of the fuse link. It is another object to provide an inexpensive but reliable fuse including a direct and ample vent for the combustion chamber together with an efficient device for indicating a ruptured fuse link and ventilating the fuse case at all times.

In my application #273,883, filed May 15, 1939, as a subsitute for my earlier application #157,288, filed August 6, 1937, for "Electric fuse, there are certain time lag and "arc blocking features described which are also indicated in the present application, but the invention herein disclosed is for further objects which include tamperproofing and economy, whereas said application No. 273,883 includes no such inexpensive structure or reliable tamperprooflng as herein disclosed, but provides an improvement to fuse links of the open or enclosed type which may be replaced or tampered with.

The object of this invention is attained by havenc'losed fuse case, which is usually hollow, tially solid and unmanageable or refractory mass of nonconducting material including a portion of the potentially fusible part of the fuse link in said mass, to prevent tampering with the value of the fuse link. The use of preformed blocks of suitable material plugged into the ends of the combustion chamber of a fuse case and cemented in position is contemplated, but so far as may be practicable and because of the economy, a cement is preferred, which will adhere with both the fusible link and the fuse case thereby forming the cement and a portion of the fusible section of the link and part of the fuse case into a permanent or non-tamperable mass which also forms an economical means for fixing the external electrical contact members in position.

For example, a mixture of plaster of Paris and water poured into an end part of the combustlon chamber of an enclosed fuse, to form a sufficient mass for the object in view, would serve the purpose quite well, but there are other materials much more difficult to tamper with, for instance a cement containing a quantity of porcelain particles would be heat conducting and extremely difficult to drill or chip or remove and when the aforementioned plugs or cement consist of heat conducting, flameproof material, there are desirable time lag and are blocking features provided.

When an enclosed fuse is provided with the aforesaid cement device, and the fuse link elec-' embody my invention, and Fig. 1 is a view of a cartridge fuse having terminals of the ferrule type and the case partly broken away to show the plug of tamperproofiing cement at H.

Fig. 2 is a sectional view of an inexpensive cartridge fuse which as a whole, may be used as the renewable element in a fuse case for renewable fuse links, showing cement at II plugging each end of the casing also a vent 22.

Fig. 3 is a sectional view of a cartridge fuse including features of Fig. 2, but having a stronger casing with end caps, substantial knife blade terminals, a ruptured fuse link, and a device 25 indicating a ruptured fuse.

Fig. 4 is an end view of one of the caps for finishing '25 over the outlet of the vent tube.

Fig. 5 shows an embodiment of the invention in a'screw plug fuse.

In further detail the numerals 6 each indicates a fuse casing composed of tough dielectric, that is, nonconducting material, having a combustion chamber 1, a fuse link 8 in said chamber, and said link connected to external electrical contact terminals 8 and It, also cement I l which is poured into the fuse case after the fuse link has been set in position. This arrangement is shown at Fig. 1, also at Fig. 5 where a typical screw plug fuse is shown with a screw threaded contact shell at 9 and a bottom contact at I0 and the cement I I has been poured into the combustion chamber 1 so as to present a surface 28 sloping toward the top of this fuse plug, thereby causing a rupture of the fuse link 8 where it can be clearly seen through the usual mica window 28 which is held in place by the customary top capping 30.

In the fuse cases, the surfaces that come in contact with the cement will be made adaptable for anchoring or keying both together, for instance in cases comprising fibrous material the wall surface may be lacerated as at I3, as an economical means of forming the cement and part of the fuse case into one unmanageable mass.

The fuse cases illustrated, show a considerable mass of cement, but it is to be understood that more or less of a really substantial body of cement may be used to accomplish the objects of the invention, in fact it is desirable to use the lesser amount and leave more space for the expansion of gas when the link disrupts.

The potentially fusible metal in fuse links is often completely volatilized, but a desirable amount of volatilization is not generally to be depended upon to extend up to or into the cement II and to char that end of the fuse link as previously described. It is therefore expedient to provide a. relatively short and particularly fusible section l2 intermediate the ends of the fuse link 8; and arrange all to embed a part I! of the fusible section l2 in the cement II, which makes the charrin of that end of the link more certain because a less fusible part 20 of the link is quite close or at least within arcing distance to the face IQ of the cement, then an arc can continue until part of the section I! which is embedded in the mass H, is charred as indicated by 2|, in

- Fig. 3, where it is shown that a very small portion l8 of the less fusible part 20 has burned away in continuing the are as desired.

Furthermore, by the arrangement just described, the mass of cement H cooperates with the less fusible parts of the fuse link as at. 20, in conducting heat from that part of the fusible section which extends out of the mass, and

causes the fusing thereof to be delayed, and, only cludes important time lag and are blocking fea- .1,

tures as well as tampe rproofing; I prefer that section at l2 to be substantially as shown, that is, part of a unitary strip of fuse metal, of reduced cross-section and of a length less than one quarter of the distance between the contact terminals of a National Electrical Code standard fuse gap which varies according to the rating of the fuse. For example, the standard gap for a fuse rated at 600 amperes and 600 volts, is nine inches, but in such an instance the fusible section at l2 may be considerably less than one quarter of nine inches.

In a fuse arranged as thus far described, a necessary disruption of the fuse may occur freely and promptly, an electric arc will be blocked by the mass at H, therefore the disruption will be brief and limited almost entirely to that end part of the short section l2 which extends from and clear of the mass at H; the remainder of the short section l2 being embedded in refractory dielectric material, safe from an electric arc and tampcz'proof. Also when an overload of current is tempc:ary-in other words not of harmful duration-the mass at H will naturally absorb heat from the short section at l2 and thereby effect a time lag-in other words, delay a disruption by said overload which may then subside without disrupting the fuse unnecessarily; the same delay is often asserted to be a function of a granulated filling in fuse cases, but the solid mass shown at l I is more efiective, and by blocking the electric arc, it is safe to use unusually heavy metal in the less fusible portions as shown at 20 in the fuse link 8 to further expedite the conduction of heat fromthe fusible section I! and increase the delay of a disruption.

In the cartridge fuse at Fig. 2, which may be used as the renewable element in renewable fuse cases, I have included the improvement as thus far described, and moreover the cement H is used to constitute the closure for each end of this tubular casing 6, and the same cement also provides the means for firmly fixing each end terminal 9 and 10 which are embedded in the cement H in the proper position, and in some instances Fuse elements of the type shown at Fig. 2, are

known to frequently burst because of the relatively flimsy casing having little or no venting, therefore I have provided an ample vent tube 22 which extends from the surface at the end of the. fusecase, through the cement H in which it is anchored, and into the combustion chamber 7, and that end of the vent tube 22 which extends into the combustion chamber is provided with a multiple of perforations 23 forming a screen to baffle or prevent the passage therethrough of flame and small particles, but permit the exit of expanding gas; the end of the vent tube 22 which is in the chamber I is preferably closed by pinching at 29, this tube may be made from any suitable material.

At Fig. 3, the cartridge fuse shown has terminal members 9 and ill of the knife blade type permanently fixed in the cement ll. This fuse includes the improvements previously described also the following; it is desirable that this fuse present a well finished appearance, therefore caps M and I5 composed of nonconducting material, are used on each end of this tubular casing 6 to cover the relatively crude'appearance of the cement II and it will be seen that said caps form a convenient means for assembling the fuse. Each of the caps 14 and I5 are provided with a slot I6 for the terminal blades 9 and ID and one of said caps is also provided with a hole 24 for the outlet end of the vent tube-22, and each cap has the inner surface lacerated 83 to key with the cement ll.

At Fig.3, the outlet end of the vent tube 22 is covered by a label 25 which is more distinctly shown at Fig. i, and which may be composed of paper cemented in position, said label is adapted to be broken by the pressure of a blast of expanding gas in its escape through the vent tube, thereby lndicating a ruptured fuse.

The fuse at Fig. 3, as thus far described, would normally be without secondary ventilation, therefore the indicator label 25 is provided with perforations 23, which permits heated air to be gently exhaled directly from the most heated part of the enclosed fuse; and prevents charring of the casing, which is frequently caused by the fuse carrying the maximum current for long periods.

It is to be noted that an importantly improved result is provided for by the above described vent tube and label in combination, in that, the ampie vent tube 22 has a perforated portion at 23 substantially in the middle'of the combustion chamber, or in the vicinity of a disruption; and at the outlet end of the vent tube, the label 23 constitutes a closure which is adapted to hold against the quickly expanding gas when the link is disrupted, until the pressure of gas is suiiicient to displace said closure with an expulsive blast through the tube, which results in the gas being so abruptly and copiously expelled that the extinguishment of the arc is materially promoted, and this result is partly due to the partial vacuum formed when gas is thus expelled.

In assembling the fuse at Fig. 3, the outlet end of the vent tube 22 is inserted in the hole 24 of the cap I5, then that cap, by means of the slit i6, is slipped over the terminal blade HI, and fitted on one end of the casing 6, then the cement H is poured into that end of the combustion chamber 1, the next space in the chamber 1 is then partly filled with a dry powder which may be plaster of Paris in relatively large granules 21, these granules serve to absorb the shock of a violent disruption, retard the progress of an arc, dissipate heat from the link 5, and also form a foundation for the necessary amount of cement plugging the other end of thecasing 6, where upon the cap H is slipped over the other terminal blade 9 and on that end of the casing with the lacerations ii of the cap engaging with the cement I l to anchor therewith as the cement hardens and also permanently fixes the terminals 8 and I in position, and finally the indicating labe] 25 is cemented in its place, although the indicator 25 may consist ofa perforated plug frictionally held in the outlet end of the tube 22.

It must be obvious that a fuse constructed as that at Fig. 3, is less expensive to manufacture and more safe to handle than the usual fuse, because the usual metal end closures or ferrules have been eliminated and a minimum of metal is exposed, consequently reducing the possibility of bridging end ferrules with extra fuse metal and also reducing accidental electric shock when handling the fuse; and furthermore to tamper with this fuse, is very impractical and less economical than with more expensive enclosed fuses.

It is not deemed necessary to show all of the fuses to which this invention is applicable, and several modifications are contemplated to suit particular requirements or methods of manufacture, all of which are believed to be within the scope of the appended claims.

Iclaim:

' 1. In an enclosed electric fuse, the combination of a fuse link having a section equal to less than half its length so constructed as to be a particularly fusible section of the link, and, a dielectric casing having a substantial portion thereof arranged to form a refractory solid mass which includes at least half of said fusible section of the link to substantially prevent the fusing thereof, and prevent tampering with the value of the fuse link, the remainder of said fusible section of the link extending from said mass whereby, a disruption of the fuse link may be limited substantially to said remainder of the fusible section by said mass blocking an electric arc close to the disruption.

2. In an enclosed fuse, the combination of a casing having contact terminals, a strip of fusible metal having a relatively short section thereof, intermediate its end portions, reduced in cr0ss-section and particularly fusible; and, a substantial body of material which is heat conducting, dielectric, and solid, arranged to form with said casin and a portion of said particularly fusible section a refractory mass, an end portion of said short and particularly fusible section extending from said mass.

the strip,

3. In an enclosed fuse, the combination of a casing having contact terminals, a strip oi. fusible metal having a relatively short section thereof intermediate its end portions reduced in crosssection and particularly fusible, and, a body of heat conducting dielectric cement poured into an end of said casing and therewith forming a solid refractory mass which includes a cross-section of the casing and a substantial portion of said short and particularly fusible section of a portion of said short and particularly fusible section extending from said mass; whereby, heat may be conducted from said short section to retard fusing thereof, and a disruption in said strip may be limited substantially to said portion of the short section extending from said mass, and also a portion of said short section may be held in said mass safe from an electric arc and safe from tampering therewith.

4. In an enclosed fuse, the combination of a casing having contact terminals, a fusible strip having a section thereof which is more fusible and located intermediate less fusible portions of the strip, and, a body of material which is heat conducting, dielectric, solid, flameproof, and arranged to form with said casing and a portion of said more fusible section an unmanageable mass, one of said less fusible portions of the strip being within arcing distance of said mass with a relatively short portion of said more fusible section therebetween whereby, the less fusible portions of the strip and said mass cooperate to absorb heat from the more fusible section and retard the fusing thereof, and induce an arc to char and render unmanageable the end of the fusible section which is in said unmanageable mass, and the mass substantially limits a disruption of said fusible strip to that portion of the fusible section between the mass and the less fusible portion of strip by blocking an electric are close to the beginning of a disruption.

5. In an enclosed cartridge fuse, the combination of a tubular casing having contact terminals and a combustion chamber, a strip of fusible metal having a relatively short section thereof reduced in cross-section and more fusible, and, a body of material which is heat conducting, dielectric,- and refractory, and arranged in an end of said casing to form a refractory mass which includes a cross-section of the casing and an end part of said more fusible section of the trip, an end part of said more fusible section extending from said mass, a vent comprising a tube having a perforated portion, said tube being secured in position by said mass and extending through the mass with an end of the tube at the exterior of the fuse and said perforated portion within the combustion chamber of the fuse.

6. In an enclosed fuse having a casing provided with a combustion chamber, a fuse link therein, and contact terminals; a vent for said combustion chamber comprising, a hollow tube having a portion thereof provided with a multiple of perforations adapted to permit gas to pass therethrough and prevent the passage flame, said tube having an end at the external surface of said casing and a perforated portion within said combustion chamber,

' 7. In a cartridge fuse, a vent for the combustion chamber comprising a tube having a screened end in the combustion chamber and a perforated fragile cover on the outlet end.

8. A cartridge fuse comprising a tubular casing, an end of said casing closed by means-of nonconducting material, a flame baffling vent tube through said material and a perforated fragile cover over the outlet of said vent.

9. In a cartridge iuse having tubular casing, contact terminal, a combustion chamber, and a fuse link therein; a vent for said combustion chamber comprising, a hollow tube having a portion provided with perforations, and adapted to copiously vent gas and prevent the passage of flame, said tube having an outlet at the end of said casing and a perforated portion substantially 10 in the middle of said combustion chamber, in combination with a closure for said outlet or the tube, said closure being adapted to hold against quickly expanding gas until the pressure of gas issuilicient to displace said closure with an expulsive blast whereby. when said link is disrupted gas is abruptly and copiously expelled and ex:- tinguishment of the are promoted.

FRANKLIN S KLEIN. 

